1. Field of the Invention
The present invention relates to a television image display apparatus for controlling the video output of a television receiver or the like in a manner to achieve a desired image quality for each field.
2. Description of the Prior Art
In a video output circuit of a television receiver or the like, a variety of output signal control devices are provided, for example, for adjusting the luminance level (brightness and contrast), color level, sharpness and the like of an image on a display screen, and such control devices are normally adjusted by the user.
The image state on the display screen continuously changes depending on the content of each video program, so that, even if the described control devices are adequately adjusted for one program so as to attain the best image quality thereof, it does not ensure that the image quality will remain optimum for a different program. Thus, for example, since visual impressions of displayed images vary significantly with regard to extremely light and dark scenes, maintaining a proper luminance level is difficult. Therefore, if a luminance adjustment is performed during a light video output, the luminance level normally tends to be adjusted by the user towards a slightly darker image. After such luminance adjustment is completed and fixed by the user, the contrast and so forth are thereafter controlled on the basis of such fixed luminance level. Such a fixed luminance level produces an image with "black deformation" or "black separation", which is unsatisfactory, when the video output is changed from a light to a dark video output. Thus, maintaining the best state of the displayed image is difficult.